1. Field of the Invention
The present invention relates to a chain for rolling elements, and more particularly to a chain for holding the rolling elements of a motion transmission apparatus.
2. Description of the Prior Art
Referring to FIGS. 9A and 9B, a conventional chain structure for a motion transmission apparatus comprises includes a plurality of spacers 511 and two links 512 at both sides of the respective spacers 511 for connecting them together so that a plurality of rolling elements 11 roll within the spaces defined by the spacers 511 and the links 512. If this conventional chain structure is an assembly structure, it will cost a lot of time and manpower to assemble spacers 511 and the links 512 together into a chain structure. If the spacers 511 are unitary with the links 512, the spacers 511 are concave structures from the point of view of mold design, which will lead to the occurrence of undercut during demolding. Forced demolding has a size restriction and might cause deformation of the product to be formed.
Referring then to FIG. 10, another conventional chain structure 61 for holding the rolling element 11 comprises a plurality of spacers 611 and two links 612 connected at both sides of the spacers 611. The disadvantage of this conventional chain structure is that, during injection molding, a thin and long cylindrical member must be used as a core in order to form the circular aperture 613 in the respective spacers 611, and after forming of the product, it has to use a complicated transmission mechanism to push or pull out the cylindrical member. However, the formed product will tightly embrace the cylindrical member after cooling off, making it difficult to pull out the cylindrical member. Meanwhile, the pulling action might cause deformation of the formed product, and the cylindrical member is likely to deform after being repeatedly pulled out and pushed back. Furthermore, during injection molding, the injection pressure is so great that the thin and long cylindrical member is very much likely to deform or break. Hence, this chain structure 61 as shown in FIG. 10 is not suitable for mass production, and the mold design and manufacturing cost is high.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.